Fuse cutouts are known in the art. In electrical distribution systems, a fuse cutout is a combination of a fuse and a switch found primarily in overhead feeder lines to protect distribution circuits and transformers from current surges and overloads. An overcurrent caused by a fault in the transformer or customer circuit will cause the fuse to melt, disconnecting the transformer from the line. To facilitate disconnection, cutouts are typically mounted about 20 degrees off vertical so that the center of gravity of the fuse holder is displaced and the fuse holder will rotate and fall open under its own weight when the fuse blows. Mechanical tension on the fuse link normally holds an ejector spring in a stable position. When the fuse blows, the released spring pulls the stub of the fuse link out of the fuse holder tube to reduce surge duration and damage to the transformer and fuse holder to quench any arc in the fuse holder. The cutout can also be opened manually by utility linemen standing on the ground and using a long insulating stick called a “hot stick”. If equipped with appropriate mechanisms, cutouts can act as sectionalizers, used on each distribution line downstream from autoreclosing circuit breakers. Autoreclosers sense and briefly interrupt fault currents, and then automatically reclose to restore service. Meanwhile, downstream sectionalizers automatically count current interruptions by the recloser. When a sectionalizer detects a preset number of interruptions of fault current (typically 3 or 4) the sectionalizer opens (while unenergized) and remains open, and the recloser restores supply to the other non-fault sections.
A fuse cutout comprises three major components. The first component is the cutout insulator body, a generally open “C”-shaped frame that includes a conductive top hood piece and a conductive bottom hinge pieces which cooperate to accept a fuse holder as well as a ribbed porcelain or polymer insulator main portion that electrically isolates the conductive portions from the support bracket to which the insulator is fastened via a centrally extending mounting flange. The second component is the fuse holder itself, also called the “fuse tube”, that is an insulating tube which contains the replaceable fuse element. When the fuse element operates (“melts”), the fuse holder subsequently drops out of the upper contact of the top hood of the insulator body, breaking the circuit, and hangs from a hinge on its lower end that cooperates with the bottom hinge of the insulator body via a pinion. The hanging fuse holder provides a visible indication that the fuse has operated and assurance that the circuit is open. The circuit can also be opened manually by pulling out the fuse holder using a hot stick with approved load break device. The third component is the fuse element, or “fuse link”, which is the replaceable portion of the cutout assembly that operates when the electrical current is great enough. In operation, after the fuse link has blown and the fuse holder drops, a lineman replaces the fuse link and re-deploys the fuse tube in its operating condition between the conductive top hood and bottom hinge pieces of the fuse cutout insulator body.
Today, two types of prior art cutout insulator bodies are used in the field: porcelain and polymer. Porcelain cutout bodies are configured by taking a solid piece of porcelain and boring three holes in the porcelain to accept metal pins that are then used to hold the metal pieces (e.g., top hood, bottom hinge, and central mounting flange) of the cutout in their proper position. A sealing agent, such as sulpher-based cement or similar known material is used to hold and seal the body. The porcelain-based cutout suffers from the drawback of a limited lifespan due to aging problems characterized by the porcelain being compromised and necessitating replacement. This problem is exacerbated in northern climates where the hot and cold seasons result in concomitant expansion and contraction of the component materials which, especially in the presence of moisture, may lead to cracked or punctured porcelain.
A more recent design in the art makes use of polymer cutouts. As will be appreciated, in traditional polymer cutouts, a fiberglass rod is used as a base material to which the metal pieces of the cutout are crimped into place. Injection molding is then used to mold weathersheds around the rod assembly and seal the insulator body. The cost of the material (and price differential) detracts from their deployment in many circumstances. In addition, some polymer cutouts may have their own potential drawbacks, particularly, resulting from interface flaws inevitable with the mass production of injection molded products. With polymer cutouts, the interface flaws result in “tracking”—wherein the dielectric material and carbon-tracking rise to a point of “flash over”—resulting in a short circuit of the device.
The foregoing underscores some of the problems with conventional fuse cutouts.